尿素合成塔衬里外壁开裂原因分析

Analysis on Cracking Reason for Liner Material of Some Urea Synthetic Tower

采用光学显微金相、X射线衍射、扫描电镜及能谱等方法,分析了某厂尿素塔衬里外壁开裂原因。实验表明,由于衬里外壁在氨气检漏过程中形成特定腐蚀环境,使得316L钢固溶处理后残留的粗大Fe-Cr-Ni-Mo相和铁素体相发生点蚀形成应力集中源,焊接过程中造成热影响区局部σ相析出、脆化以及残余拉应力状态,三者共同作用下导致尿素合成塔外壁在长期服役过程中发生应力腐蚀开裂。

The cracking reasons for the liner material of some urea synthetic tower were analyzed using optical microscopy, XRD, SEM and EDS. The results show that the corrosive environment forms between liner material and veneer sheet during the ammonia leak detection process and results in the pitting of Fe-Cr-Ni-Mo phase and ferrite phase which remained in the 316L stainless steel after solution treatment. The combined effect of precipitation embrittlement of σ phase and residual tensile stress were caused by welding process, and stress concentration at the pitting causes stress corrosion cracking of the urea synthetic tower.